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| Titel |
2D and 3D rockfall simulations of a real-size experiment on weathered volcanic hillslopes in Tahiti, French Polynesia |
| VerfasserIn |
Christian Mathon, Hiromi Kobayashi, Olivier Sedan, Aude Nachbaur, Thomas Dewez, Frédéric Berger, Emmanuel Des Garets |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250035113
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| Zusammenfassung |
| The Land Planning Authority of French Polynesia contracted BRGM to run a real-size
rockfall experiment, called OFAI, in September 2009. The purposes of the experiments are
two fold : first observe real-size rock trajectories in a context of variably weathered volcanic
rock slopes; and second, use observed rockfall trajectories to calibrate block propagation
models. 90 basalt blocks were dropped down a 150-m-long slope made of hard
basalt veins, lenses of colluvium and erosion channels covered in blocks of various
sizes. Parameters of the experiment concerned the shape (from nearly perfect sphere
to elongated cubes) and mass of the blocks (from 300 kg to >5000 kg), and the
launching point, in order to bounce the blocks both off stiff basalt veins and colluvium
lenses.
The data obtained from this real-size experiment were analyzed using two rockfall
simulation models: a 2D model developed by the University of British Columbia, the
Geological Survey of Canada and BRGM, and a 3D model which was developed from the 2D
model, with the purpose of integrating the lateral dispersion of rockfalls. Both models are
characterized by a “hybrid approach” with a lumped mass assumption, taking indirectly the
shape and rotational momentum of the block into account. Bouncing is simulated using soil
restitution coefficients and plastic impact model (Falcetta, 1985). The input data are defined
by probability density functions, thus allowing for both deterministic and probabilistic
analysis. Usually calibrated with rare and punctual rockfall events, this recent experiment
gave us a complete inventory of real 3D trajectories, associated with precise descriptions
of the blocks (mass, shape) and accurate geomorphological characteristics of the
impact points, so as to assess the performance of both models. The aims of the
simulations were (i) comparing real trajectories to the simulated ones and evaluating their
reliabilities (ii) calibrating material parameters for weathered volcanic tropical
soils (iii) measuring the benefit from the 3D approach compared to 2D analysis.
Limits and further improvements on the models are discussed; especially, the major
influence of the spatial resolution of the Digital terrain model (DTM) was clearly
highlighted. |
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